--- a/toolkit/components/url-classifier/Classifier.cpp
+++ b/toolkit/components/url-classifier/Classifier.cpp
@@ -687,30 +687,30 @@ LookupCache *
 Classifier::GetLookupCache(const nsACString& aTable)
 {
   for (uint32_t i = 0; i < mLookupCaches.Length(); i++) {
     if (mLookupCaches[i]->TableName().Equals(aTable)) {
       return mLookupCaches[i];
     }
   }
 
-  LookupCache *cache = new LookupCache(aTable, mStoreDirectory);
+  UniquePtr<LookupCache> cache(new LookupCache(aTable, mStoreDirectory));
   nsresult rv = cache->Init();
   if (NS_FAILED(rv)) {
     return nullptr;
   }
   rv = cache->Open();
   if (NS_FAILED(rv)) {
     if (rv == NS_ERROR_FILE_CORRUPTED) {
       Reset();
     }
     return nullptr;
   }
-  mLookupCaches.AppendElement(cache);
-  return cache;
+  mLookupCaches.AppendElement(cache.get());
+  return cache.release();
 }
 
 nsresult
 Classifier::ReadNoiseEntries(const Prefix& aPrefix,
                              const nsACString& aTableName,
                              uint32_t aCount,
                              PrefixArray* aNoiseEntries)
 {